Fix possible crashes in QDeclarativeRadioData.

It would crash when accessing any of its properties when there is no
radio backend available.

Task-number: QTBUG-47859
Change-Id: Ic7c0a70ca3e9a4768359b3429ea812caece09fce
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>

src/imports/multimedia/qdeclarativeradiodata.cpp

@@ -129,7 +129,10 @@ QDeclarativeRadioData::~QDeclarativeRadioData()
  */
 QDeclarativeRadioData::Availability QDeclarativeRadioData::availability() const
 {
-    return Availability(m_radioData->availability());
+    if (m_radioData)
+        return Availability(m_radioData->availability());
+
+    return Unavailable;
 }
 
 
@@ -141,7 +144,10 @@ QDeclarativeRadioData::Availability QDeclarativeRadioData::availability() const
   */
 QString QDeclarativeRadioData::stationId() const
 {
-    return m_radioData->stationId();
+    if (m_radioData)
+        return m_radioData->stationId();
+
+    return QString();
 }
 
 /*!
@@ -206,7 +212,10 @@ QString QDeclarativeRadioData::stationId() const
   */
 QDeclarativeRadioData::ProgramType QDeclarativeRadioData::programType() const
 {
-    return static_cast<QDeclarativeRadioData::ProgramType>(m_radioData->programType());
+    if (m_radioData)
+        return static_cast<QDeclarativeRadioData::ProgramType>(m_radioData->programType());
+
+    return Undefined;
 }
 
 /*!
@@ -216,7 +225,10 @@ QDeclarativeRadioData::ProgramType QDeclarativeRadioData::programType() const
   */
 QString QDeclarativeRadioData::programTypeName() const
 {
-    return m_radioData->programTypeName();
+    if (m_radioData)
+        return m_radioData->programTypeName();
+
+    return QString();
 }
 
 /*!
@@ -226,7 +238,10 @@ QString QDeclarativeRadioData::programTypeName() const
   */
 QString QDeclarativeRadioData::stationName() const
 {
-    return m_radioData->stationName();
+    if (m_radioData)
+        return m_radioData->stationName();
+
+    return QString();
 }
 
 /*!
@@ -238,7 +253,10 @@ QString QDeclarativeRadioData::stationName() const
   */
 QString QDeclarativeRadioData::radioText() const
 {
-    return m_radioData->radioText();
+    if (m_radioData)
+        return m_radioData->radioText();
+
+    return QString();
 }
 
 /*!
@@ -250,12 +268,16 @@ QString QDeclarativeRadioData::radioText() const
   */
 bool QDeclarativeRadioData::alternativeFrequenciesEnabled() const
 {
-    return m_radioData->isAlternativeFrequenciesEnabled();
+    if (m_radioData)
+        return m_radioData->isAlternativeFrequenciesEnabled();
+
+    return false;
 }
 
 void QDeclarativeRadioData::setAlternativeFrequenciesEnabled(bool enabled)
 {
-    m_radioData->setAlternativeFrequenciesEnabled(enabled);
+    if (m_radioData)
+        m_radioData->setAlternativeFrequenciesEnabled(enabled);
 }
 
 void QDeclarativeRadioData::_q_programTypeChanged(QRadioData::ProgramType programType)